Rotaxanes from Tetralactams

Attempts to incorporate a tetralactam (3a) into a side-chain polyrotaxane by formation of its complex with p-tritylphenolate and reaction with poly­(vinybenzyl chloride) failed, probably due to steric hindrance. However, three new small molecule model rotaxanes (acetal 11a and ethers 14a and 14b) were prepared based on this macrocycle, and one (14b) was characterized by X-ray crystallography. Attempts to prepare poly­(ether rotaxane)­s such as 18 and 20b via polymerizations in the presence of this tetralactam failed because the mild conditions required for complexation (nonpolar solvent, room temperature) are not sufficient for effective step-growth polymerizations, resulting in only oligomer formation. In an alternative approach, clipping of the tetralactam 23 onto a preformed poly­(urethane rotaxane) (27) in CH2Cl2 was successful, and the original biphasic segmented polymer was converted to a single-phase polyrotaxane (28) with a significantly lower glass transition temperature.